1. Field of the Invention
This invention relates to concealed fastening roof structures, and more particularly to improved panel support assemblies which provide consistent and accurate control of the panel module during erection, and which permit two or more courses of the panel members to move as a unit during thermal expansion and contraction.
2. Description of the Prior Art
Virtually all profiled panel members are fabricated by roll forming operations to established manufacturing tolerances to provide, for example, a 36" (91.44 cm) coverage width. However, the actual coverage width of the panel members may deviate from the intended 36" coverage width, by as much as .+-.3/16" (.+-.0.476 cm). The deviations may be caused by clearances in the rolls of the roll forming equipment, which is necessary to accomodate various gauges of the sheet metal and decorative coating thickness and by coil-to-coil variations in the physical properties of the steel. These roll clearances and the physical property variations introduce varying degrees of permanent set and spring back in the material being roll formed thereby causing variations in the final shape of the ribs, and hence, in the coverage width.
Since the panel coverage cannot be precisely controlled at the time of manufacture, the roof installation must be engineered assuming a 36" coverage width. The panels must be installed so as to provide the 36" coverage width regardless of the actual manufactured panel width. This is normally accomplished in profiled panel members by "moduling" the panel member, that is by physically stretching or compressing the panel member to conform its width to the engineered width.
Concealed fastening roof systems are known which employ locator strips for precisely locating the concealed fasteners at a uniform spacing, see for example U.S. Pat. Nos. 3,716,958 (SCRIVNER) and 4,285,182 (DINGES). In erecting such systems, the erector can only maintain the intended panel module. The modular width of the panel cannot be adjusted to accommodate differences between the "as engineered" dimensions and the "as built" dimensions of the steel framing.
My copending application number 376,169 filed May 7, 1982, now U.S. Pat. No. 4,486,998, and assigned to assignee of this invention, discloses and claims a system by which "moduling" of the panel members may be consistently and accurately achieved. The system utilizes one fixed clip and two or more floating clips per panel member. The disclosed system relies on precisely locating the fixed clips to achieve the desired moduling of the panel members. The present invention constitutes an improvement over the aforesaid copending application Ser. No. 376,169, in that the present invention provides a means for varying the distance between the fixed clips during erection of the roof structure so as to accommodate the panel coverage to the coverage required by the erected steel framework.
In conjunction with the above-noted erection requirements, the concealed fastening system also must allow the panel members to undergo thermally induced movement, that is to move as a unit during thermal expansion and contraction. Certain profiled panel members of simplified design, may be roll formed at the job site to any required length. Such single length panel members may not be subject to buckling or seal rupture during thermal movement provided that the panel members are secured to the structural steel by suitable concealed fasteners.
Most concealed fastening roof systems utilize panel members whose length is limited by plant space, handling or shipping limitations. Such limited-length panels are erected in multiple courses which present lap joints wherein the panel ends of one course overlap those of the adjacent course. At the lap joint, the panel ends tend to move in opposite directions for a given thermal condition. Such movement may shear the sealant line, elongate fastener holes or shear fasteners all of which tend to degrade the lap joint seals and to produce undesirable leaks in the roof structure. Ideally, the multiple panel lengths should be joined in such a way that the multiple lengths respond to thermal inputs as would a single elongated sheet. This requires the lap joint condition to move as a unit and in a single direction rather than having the panel ends move in opposite directions. Many concealed fastening systems ignore thermally induced movement at the lap joints.
In other systems, the lap joint is spaced from the adjacent panel support assembly or the purlin so that the lap joint fasteners can move with the lap joint independently of the support. This approach results in an inherently weak end lap for one or more of the following reasons. The concealed fastener must physically contact the panel member in order to anchor it to the structural steel. Such contact results in frictional drag as thermal conditions cause the panels to expand and contract and slide past the concealed fastener. If the frictional resistance of the concealed fasteners on opposite side of the lap joint differ substantially, the panel ends undergo different rates of thermal expansion whereby the panel ends move in opposite directions. The end result is the same. That is, such movement may shear the sealant line, elongate fastener holes or shear fasteners thereby degrading the lap joint seal and causing undesirable roof leaks. As a further consideration, locating the end lap condition away from the support drastically increases the likelihood of damage to the lap joint fastening and to the sealant due to foot traffic and other live loads since no firm foundation exists beneath the lap joint to resist these forces. In addition, locating the lap joint condition away from a support creates a weak line of bending resistance since the overlapped sheets cannot be clamped effectively enough to produce the equivalent bending resistance of an unbroken sheet section.